1. Field of the Invention
The present invention relates generally to a trouble detection apparatus for air-conditioner, and particularly concerns a trouble detection apparatus for air-conditioner comprising an overcurrent detection circuit.
2. Description of the Prior Art
In recent years, energy saving in an air-conditioner system has become desirable. Accordingly, a modern trend has included employing a variable speed compressor to be operated by a variable frequency inverter in the air-conditioner. One conventional air-conditioner comprising such variable speed compressor operated by the variable frequency inverter is elucidated with reference to FIG. 1 which is a circuit block diagram of the main part of the air-conditioner, and FIG. 2 which is a time chart for elucidating operation of the circuit of FIG. 1.
In the conventional air-conditioner apparatus of FIG. 1, an AC current is received, through a rush current prevention reactor L1, by a full wave rectifier circuit 12 consisting of four diodes D1, D2, D3 and D4, and capacitors C1 and C2 connected in series for double, or full wave, voltage rectifying and a smoothing capacitor C3. The full-wave voltage-rectified voltage across the capacitor C3 is coupled through a resistor R1 to an inverter 2 comprising six transistors Q1, Q2, Q3, Q4, Q5 and Q6 and diodes D5, D6, D7, D8, D9 and D10. The bases of the transistors Q1 through Q6 receive control signals from a switching control circuit 6 of a control part 30, to control ON and OFF states of the transistors Q1 through Q6, to thereby generate AC current of a necessary frequency. The output AC current of the inverter 2 is fed to a compressor 7. Accordingly, the compressor 7 is driven at a rotation speed defined by the control signals from the switching control circuit 6.
Operation of the above-mentioned conventional air-compressor is as follows. When the compressor 7 or any of the transistors Q1 through Q6 of the inverter 2 becomes faulted, the current flowing through the resistor R1 increases, thereby increasing voltage thereacross. Then, the increase of the voltage causes the comparator 3 to issue an output signal to the logic circuit 4, and the logic circuit 4 issues a signal to the switching control circuit 6, thereby to stop generation of the AC current by the inverter and to stop the compressor 7.
In the waveform (A) of FIG. 2 showing inverter current, a peak 21 indicates a time of detection of inverter current exceeding a predetermined value (e.g., 28 A), at which the compressor 7 is stopped. Then a pause timer 5 of the control part 30 induces the switching control circuit 6 to make the compressor motor 7 stop for a predetermined time T (for instance, about 3 minutes) which is necessary for stabilization of refrigerant circuit for next starting. That is, when the DC current flowing into the inverter 2 increases as a result of overcurrent of the compressor 7, the overcurrent is detected by the control part 30, and stops the compressor 7 for the predetermined pause time period T. After a lapse of the pause time of T, the compressor is re-started with a stabilized state of the refrigerant circuit, and operates.
However, in case of a trouble of the compressor 7 or trouble of any of the transistors Q1 through Q6, the overcurrent above the predetermined value is again detected at the current value 22 of the waveform (A) of FIG. 2 within a predetermined longer time t.sub.1. Then the logic circuit determines that it is more than a spurious problem in the compressor 7, and the compressor is permanently stopped. Thereafter, until a manual operation is initiated to make the circuit re-start the compressor, the compressor is retained in stopped mode, pending a thorough checking of the system. The above-mentioned longer time period t.sub.1 is also defined by the timer 5. In the above-mentioned conventional circuit of FIG. 1, since the predetermined longer time t.sub.1 is defined very long, such as 30 minutes, there is a liability that receiving of noises by the logic circuit 4 thereby making the switching control circuit 6 stop the compressor 7 irreversibly, even though there is no real trouble in the compressor 7 or any of the transistors Q1-Q6. Accordingly, the conventional air-conditioner has had a shortcoming that the air compressor is likely to be irreversibly stopped without actual necessity, thereby making the user uncomfortable.